SELECT 
  * 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variant_descriptions.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'es' 
WHERE 
  cscart_product_feature_variants.variant_id = 127

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.00"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variants",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
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            "eval_cost": "0.20",
            "prefix_cost": "0.00",
            "data_read_per_join": "1K"
          },
          "used_columns": [
            "variant_id",
            "feature_id",
            "url",
            "color",
            "position"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_product_feature_variant_descriptions",
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          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
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          "rows_examined_per_scan": 1,
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          "used_columns": [
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            "description",
            "page_title",
            "meta_keywords",
            "meta_description",
            "lang_code"
          ]
        }
      }
    ]
  }
}

Result

variant_id feature_id url color position variant description page_title meta_keywords meta_description lang_code
127 18 0 Swingline <p><b>Swingline</b> is a division of ACCO Brands Corporation that specializes in manufacturing staplers and hole punches. The company was formerly located in Long Island City, Queens, New York, United States, but is now headquartered with its parent company ACCO in Lincolnshire, Illinois.<br></p> es